1. Field of the Invention
This invention relates to an improved process for separating hydrocarbons into fractions having different boiling points. More particularly, this invention relates an improvement in a distillation process.
2. Description of Information Disclosures
Processes are known for separating mixtures of hydrocarbons into fractions having different boiling point ranges by subjecting the hydrocarbon mixture to a distillation zone to produce a vapor phase fraction, one or a plurality of liquid sidestreams, and a heavy bottoms fraction and in which processes one or more of the liquid sidestreams is passed to additional separation zones which may be stripping zones. It is also known to recycle the vapor product of these additional separation zones to the distillation zone (i.e. the main or first distillation zone).
U.S. Pat. No. 4,702,819 discloses a process for separating hydrocarbon mixtures in which a vapor sidestream and a bottoms liquid stream resulting from a first fractionation zone are introduced into a second fractionation zone. The overhead vapor stream of the second fractionation zone is recovered.
U.S. Pat. No. 4,415,443 discloses passing a bottoms liquid stream and an overflash sidestream from a first distillation tower to a second distillation tower. Both distillation towers comprise stripping zones. The vapor of the second distillation tower is introduced into the lower portion (stripping zone) of the first fractionation tower.
U.S. Pat. No. 4,662,995 discloses a method and apparatus for separating hydrocarbon mixtures by distillation, steam stripping a sidestream, returning a vapor separated in the sidestream stripper to the distillation zone at a location at least two trays and/or at least one theoretical stage above the liquid draw-off from the distillation zone to the sidestream stripping zone.
Although some of these processes increase the amount of lower boiling components that can be separated from the heavier fractions, there is still a need to improve the separation of lower components from the higher boiling components.
It has now been found that the amount of lower boiling components that can be separated from higher boiling components can be increased or the rate of removal of the lower boiling components from the distillation can be increased, in a hydrocarbon separation process, by passing at least a portion of the vapor phase fraction of the distillation zone to a separation zone in which a liquid sidestream fraction is separated in the presence of a stripping gas, and returning the resulting stripped vapor to the distillation zone.